(8) Stock-based Compensation Plans

Effective May 19, 2004, the Company adopted its 2004 Incentive Stock Plan, as further amended and restated on February 3, 2015 (the “2004 Stock Plan”), and its 2004 Restricted Stock Plan for Non-Employee Directors, as further amended and restated on April 1, 2013 (the “Director Plan”). On May 19, 2015, the Company’s stockholders approved the 2015 Incentive Plan of 3D Systems Corporation (the “2015 Plan” and, together with the 2004 Stock Plan, the “Incentive Plans”).

The 2004 Stock Plan authorizes shares of restricted stock, restricted stock units, stock appreciation rights and the grant of options to purchase shares of the Company’s common stock. The 2004 Stock Plan also designates measures that may be used for performance awards.

The Director Plan authorizes shares of restricted stock for non-employee directors of the Company.

The 2015 Plan authorizes shares of restricted stock, restricted stock units, stock appreciation rights, cash incentive awards and the grant of options to purchase shares of the Company’s common stock. The 2015 Plan also designates measures that may be used for performance awards.

Generally, awards granted prior to November 13, 2015 become fully-vested on the three-year anniversary of the grant date and awards granted after November 13, 2015 will vest one third each year over three years.

The Company records stock-based compensation expense in selling, general and administrative expenses in the condensed consolidated statements of operations and comprehensive income (loss). Stock-based compensation expense for the quarters and six months ended June 30, 2016 and 2015 was as follows:


	Quarter Ended June 30,				Six Months Ended June 30,
(in thousands)	2016		2015		2016		2015
Stock-based compensation expense	$	7,226	$	9,721	$	18,893	$	20,050

Restricted Stock

The number of shares and units of restricted common stock awarded and the weighted average fair value per share and unit for the quarters and six months ended June 30, 2016 and 2015 were as follows:


	Quarter Ended June 30,
	2016			2015
(in thousands, except per share amounts)	Number of Shares/Units	Weighted Average Fair Value		Number of Shares/Units	Weighted Average Fair Value
Restricted stock awards granted under the:
Incentive Plans — non-executive employees, service condition	85	$	12.33	226	$	22.68
Incentive Plans — non-executive employees, market and service condition	46		12.33	—		—
Incentive Plans — executive officers, service condition	150		15.12	25		22.61
Incentive Plans — executive officers, market and service condition	75		15.12	—		—
Incentive Plans — non-employee directors	39		12.78	—		—
Director Plan — non-employee directors	24		12.78	24		22.61
Total restricted stock awards	419	$	13.90	275	$	22.67

	Six Months Ended June 30,
	2016			2015
(in thousands, except per share amounts)	Number of Shares/Units	Weighted Average Fair Value		Number of Shares/Units	Weighted Average Fair Value
Restricted stock awards granted under the:
Incentive Plans — non-executive employees, service condition	85	$	12.33	439	$	25.86
Incentive Plans — non-executive employees, market and service condition	46		12.33	—		—
Incentive Plans — executive officers, service condition	150		15.12	85		27.50
Incentive Plans — executive officers, market and service condition	75		15.12	—		—
Incentive Plans — non-employee directors	64		10.79	—		—
Director Plan — non-employee directors	24		12.78	24		22.61
Total restricted stock awards	444	$	13.55	548	$	26.00

Stock Options

The Company estimates the fair value of stock options and restricted stock awards with market conditions using a binomial lattice Monte Carlo simulation model. The weighted-average fair value and the assumptions used to measure fair value were as follows:


	Quarter Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
Stock option assumptions:
Weighted-average fair value	$	7.54	$	—	$	7.54	$	—
Expected volatility		60.0%		—		60.0%		—
Risk-free interest rate		0.76%-1.46%		—		0.76%-1.46%		—
Expected dividend yield		0%		—		0%		—
Derived term in years		3-4		—		3-4		—

Stock option activity for the six months ended June 30, 2016 was as follows:


	Six Months Ended June 30, 2016
(in thousands, except per share amounts)	Number of Shares	Weighted Average Exercise		Weighted Average Remaining Term (in years)
Stock option activity:
Outstanding at beginning of period	—	$	—
Granted	720		14.27
Exercised	—		—
Forfeited and expired	—		—
Outstanding at end of period	720	$	14.27	10
Exercisable at end of period	720	$	14.27	10